H2 Blockers

What are H2 blockers (H2 antagonists)?

H2 blockers (H2 antagonists) are a class of drugs that suppress acid production in your stomach. Stomach acid is essential to a healthy digestive system because it breaks down the food you eat. But too much stomach acid can damage the tissue lining your GI (gastrointestinal) tract. It can cause stomach pain and heartburn — and a host of other symptoms that can make you regret eating that last meal.

If you’re powering through symptoms tied to excess stomach acid, you may want to reach for an H2 blocker.

What conditions do H2 blockers treat?

H2 blockers treat conditions related to excess stomach acid production. But they gradually lose their effectiveness when you use them consistently over time.

If you have a chronic condition related to excess stomach production, you should consider a proton pump inhibitor (PPI) instead. The effects of PPIs don’t kick in as fast as H2 blockers. But PPIs also suppress stomach acid production, and you can take them for longer. PPIs are more powerful acid blockers.

H2 blockers treat:

• Stomach ulcers: Excess stomach acid can eat away at your stomach lining, causing ulcers to form. By suppressing stomach acid production, H2 blockers allow stomach ulcers time to heal.
• Duodenal ulcers: Stomach acid can seep into the first part of your small intestine (duodenum) and cause ulcers. Although PPIs are more effective treatments for duodenal ulcers, H2 blockers can treat them, too. The U.S. Food and Drug Administration (FDA) has also approved H2 blockers for short-term maintenance therapy to prevent new duodenal ulcers from forming. Your provider can discuss various treatment and maintenance options with you.
• Acid reflux: With acid reflux, stomach acid travels upward from your stomach into your esophagus (food tube) and throat, causing heartburn. It can lead to inflammation in your esophagus (esophagitis). For occasional acid reflux, an H2 blocker can help. For chronic acid reflux (GERD), try a PPI instead.
• Zollinger-Ellison syndrome: With this extremely rare condition, tumors cause your stomach to release too much stomach acid. H2 blockers can help by counteracting stomach acid production. But your healthcare provider is more likely to prescribe a PPI.

H2 blockers provide relief from symptoms associated with these conditions, including:

• Indigestion.
• Stomach pain.
• Heartburn and reflux.
• Nausea and vomiting.
• Sour stomach.

How do H2 blockers work?

The other name for H2 blockers — histamine-2 (H2) antagonists — provides clues about how they work. Remember learning in school (maybe English class) that the antagonist’s role in a story was to create an obstacle of some sort? H2 antagonists create obstacles for acid production.

After you eat, your body releases H2. The H2 binds to the H2 receptors on the cells lining your stomach. The binding triggers a chain reaction that causes your stomach to secrete stomach acid.

When you take an H2 antagonist, the drug binds to the H2 receptors in your stomach cells so that H2 can’t attach. H2 antagonists/blockers essentially “block” H2 from binding, reducing stomach acid production.

You’ll still be able to digest food. You just won’t have excess stomach acid causing painful symptoms.

What drugs are H2 blockers?

You can get H2 blockers over the counter (OTC) or with a prescription (Rx), depending on the brand and dosage. The list of H2 blockers includes:

• Cimetidine (Tagamet^®): Available OTC and by Rx (prescription).
• Famotidine (Pepcid^®): Available OTC and by Rx.
• Nizatidine (Axid^®): Available by Rx only.

Ranitidine (Zantac^®) was the first FDA-approved H2 blocker. It became available in 1983. In April 2020, the FDA requested that manufacturers remove ranitidine from the market. FDA testing showed that levels of a potentially cancer-causing substance (nitrosodimethylamine, or NDMA) increased to unsafe levels over the shelf life of ranitidine. Researchers also discovered that storing ranitidine in high temperatures increases NDMA levels.

How do you take them?

All H2 blockers come in an oral form, which means you can take them by mouth (like a pill or capsule). Some come in powder form that you can mix with liquid if you have trouble swallowing pills. Some H2 blockers can be administered via an IV. This route can be beneficial if you’re hospitalized and unable to swallow.

When should you take an H2 blocker?

If you’re about to eat something that you know doesn’t agree with you (like a spicy dish you love), take an H2 blocker 30 to 60 minutes beforehand to give it time to work. H2 blockers can also help if you take them after the fact. But it may take an hour or so until your symptoms ease.

For short-term management of a condition like an ulcer, your healthcare provider may advise you to take them:

• Once daily at bedtime.
• Once in the morning and once at night.

If you’ve had to take an H2 blocker consistently for two weeks to manage symptoms, it’s time to schedule a visit with your healthcare provider. You shouldn’t rely on H2 blockers for long periods without talking to your provider.

How long does it take for H2 blockers to work?

It takes about an hour to experience symptom relief after taking an H2 blocker. The effects usually remain from four to 10 hours. The fast action is why it’s a good idea to try an H2 blocker if you need immediate relief or if you only occasionally experience heartburn.

For even faster relief, you can try an antacid, which neutralizes stomach acid. It’ll take effect more quickly, but the benefits won’t last as long as an H2 blocker.

If your symptoms are long-term, you may need to take a PPI, particularly if an H2 blocker isn’t helping enough. It can take one to four days to get the full benefits of taking a PPI, but the effects last much longer than an H2 blocker’s.

What are the side effects of H2 blockers?

H2 blockers provide relief with little risk of side effects. If you do experience side effects, they may include:

• Abdominal pain.
• Achy muscles.
• Constipation.
• Diarrhea.
• Dry mouth.
• Fatigue.
• Headaches.

Although it’s rare, H2 blockers may cause nervous system symptoms like confusion or slurred speech in high-risk groups. You’re more likely to experience these symptoms if you’re over 50 and have reduced kidney or liver function. Stopping the medicine usually reverses the symptoms within a few days.

Certain H2 blockers can prevent other drugs from working as effectively. For example, cimetidine may reduce the effectiveness of some SSRIs (treatment for depression) and warfarin (a blood thinner).

Speak with your healthcare provider before starting a new medication to be sure it won’t counteract the prescriptions you’re taking.

Are H2 blockers safe to take during pregnancy?

More research is needed to determine the safety of H2 blockers when taken during pregnancy. Researchers do know that this drug passes through breast (chest) milk.

Talk with your healthcare provider if you’re taking an H2 blocker and become pregnant. Ask if it’s safe to take during pregnancy or while you’re breastfeeding (chestfeeding).

When should I contact my healthcare provider?

If you find that you need to take H2 blockers consistently for two weeks to manage symptoms, you need to schedule an appointment with your healthcare provider. It’s important to diagnose what’s causing your symptoms. You may need a longer-term solution, like a PPI.

Contact your provider if you have a reaction to the medicine or notice side effects. You may need to change your dosage. Or you may need a different type of medication.

What is the safest H2 blocker to take?

FDA-approved H2 blockers are similar when it comes to both their safety and effectiveness.

Still, it’s a good idea to consult with your healthcare provider if you’re thinking of taking an H2 blocker and you’re also taking other medications. It’s important to choose a medicine that won’t interfere with the effectiveness of a medicine you’re already taking.

Which H2 blocker is best for GERD?

All H2 blockers can provide relief from acid reflux symptoms. If your acid reflux is chronic (as is the case with GERD), it may be better to steer clear of H2 blockers altogether and opt for a PPI instead. Consult with your healthcare provider for guidance.

A note from Cleveland Clinic

H2 blockers, antacids and PPIs all treat conditions related to excess stomach acid production. While it’s good to have options, the choices can feel overwhelming. Think of it this way: if what you need is short-term relief with lasting effects (several hours), H2 blockers may be your best bet. Reaching for an H2 blocker is an especially good preventive measure if you know you’re about to indulge in a meal that may make you feel the burn later. If you have any questions about which medication to choose, ask your provider.